Port Macquarie Coastal Geotrail Glossary Credits Plate tectonics Accretionary wedge is a mass of sediments and rock Authors: Ron Boyd & Robin Offler Schematic diagram showing movement of oceanic crust away from the mid-ocean ridge and down the subduction zone fragments that accumulates where one of Earth’s plates slides Editing: Simone Meakin Rocks of the Port Macquarie area tell the story of The geotrail under another, at a subduction zone. plate tectonics – how Earth’s crust is formed and how Figures: Kate Holdsworth To follow the Port Macquarie Coastal Geotrail, you Asthenosphere is the upper layer of Earth’s mantle, directly it moves. This geotrail spans the equivalent of up to Cartography: Stewart Watson can either travel in the same direction as the oceanic below the lithosphere, at depths of about 80–200 km. This 6000 km across the Pacific Ocean of today, in just Layout: Carson Cox plate was moving, from Shelly Beach and Sea Acres layer is highly viscous and deforms in a ductile manner. 4 km from Shelly Beach to Rocky Beach! Some rocks Photos: Guy Fleming and authors back to Rocky Beach and Town Beach, or you can do Blueschist is a metamorphic rock characterised by a blue, are made of microscopic marine organisms, others it in reverse. You can walk 4 km one way along the sodium-rich amphibole called glaucophane. Acknowledgements: David Och is thanked for allowing by volcanoes or underwater gravity currents. Some access to his research and photographs. Port Macquarie– geotrail, using the map to guide you. Alternatively you Clast is a rock fragment or grain resulting from the breakdown rocks formed at high pressures and temperatures, Hastings Council supplied a map, which has been modified. can drive to each stop, as they are all accessible from of larger rocks. over 100 km below Earth’s surface, and were later nearby car parks, or catch the local bus to/from Sea Conodonts are microfossils known from the Late Cambrian to © State of NSW through Department of Planning & brought to the surface by faulting. Acres Rainforest Centre. the Late Triassic. They are hard parts of an extinct group of Environment, 2018. Information in this publication is based animals believed to be distantly related to the living hagfish. Plate tectonics on knowledge and understanding at the time of writing and Timescale of major geological events Continental Eclogite is a metamorphic rock consisting of pyroxene may not be accurate, current or complete. The theory of plate tectonics is the most important in the region volcanic arc and garnet. underlying concept in geology. A network of rigid Metamorphism is the process by which rocks are physically or plates extends over Earth’s surface, to depths of Era Period Age* Geological activity chemically transformed by heat, pressure or fluids. Learn more about 100 km. The plates move relative to each Cenozoic Quaternary Today Modern beaches, estuaries Phacoid is an ellipsoidal, doubly tapered, deformed clast, other, forming and diverging at mid-ocean ridges, to 0.01 and dunes form which may have asymmetric shape. converging and, in places, being subducted at ocean Neogene to 23 and Volcanic events inland Serpentinite is a metamorphic rock composed of one or more Paleogene 24 NSW trenches. serpentine group minerals. GeoTours Mesozoic Cretaceous 72 to Seafloor spreading in the Turbidite is a sedimentary deposit of layers of particles that An oceanic crustal plate is formed at a mid-ocean 84 spreading ridge and consists of mantle rocks in the grade upward from coarse to fine sizes and were deposited by Cretaceous to 110 to Sediment accumulates in the Trench turbidity currents in the ocean. lithosphere and asthenosphere, overlain by basalt Triassic 250 Surat and Clarence–Moreton Mid-ocean ridge Download our (Stop 1) from underwater volcanoes. As the plate basins Turbidity current is an underwater current of usually rapidly free app! Explore Clastic moving, sediment-laden water moving down a slope. migrates away from the mid-ocean ridge, the basalt Mesozoic to Triassic to 237 to Coal and sedimentation in Continental crust the geotrail at Palaeozoic Permian 295 the –Gunnedah Basin sediments Accretionary Volcanic arc is a curved chain of volcanoes formed in a tectonic collects sediment on top. At first the sediment wedge your own pace, 254 Inland volcanic activity plate above a subducting plate. If offshore, it is called a with a tour guide consists mainly of microscopic marine organisms volcanic island arc. such as radiolaria, that live near the ocean surface Triassic to 201 to Inland sedimentation and at your fingertips. Carboniferous 359 granites intrude the region and fall to the seafloor to accumulate when they die E Reference Palaeozoic Permian to 260 to Marine and inland N t (Stop 2). As the oceanic plate approaches a trench O us Silurian 425 sedimentation, with rt cr Och DJ, Leitch EC & Caprarelli G, 2007. Geological units of the it also collects sediments that flow down into the volcanic activity he Z n C ea Port Macquarie–Tacking Point tract, north-eastern Port Macquarie Mantle N c Mantle trench from nearby volcanoes (Stop 3). On reaching Ordovician to 460 to Subduction zone forms, t o Block, of NSW. Quarterly Notes of the O al the trench, the denser ocean crust plate slides Cambrian 500 with associated marine I as Geological Survey of 126. (or subducts) under another plate and is carried sedimentation and T B volcanic activity C www.pmhc.nsw.gov.au/coastalgeotrail deeper down into the earth. There it is subjected to U * Millions of years ago. D increasing pressure and temperature, forming new B U TAKE CARE WHEN EXPLORING COASTAL AREAS. WILDLIFE, WEATHER, rocks and minerals such as blueschist and eclogite S Scale: at least 500 km across SURF CONDITIONS AND UNSTABLE GROUND CAN POSE RISKS. (Stops 4 and 5). Cover photo: Port Macquarie coast.

Town Beach Geological map Geotrail stops Green Mound Section through one interpretation of the Ordovician subduction zone, looking northwards across several hundred metres Oxley Beach Gordon Street Tasman Sea Continental volcanic arc Wrights Laterite, and alluvial, swamp, and dune complexes Rocky Beach

Hill Street Creek Radiolaria Mid-ocean ridge Sea Acres Dolerite: variably altered dolerite, Basalt Port Macquarie Flynns Point in places cleaved Cl Dyke astic sediment Flynns Beach s pillows Tacking Point Gabbro and Town Beach Diorite: 1 gabbro, pyroxenite, diorite, pegmatite Coastal Geotrail Flynn St Continental ts en Nobbys Beach crust m New South Wales Sedi Touchwood Formation: siltstone, sandstone, paraconglomerate, breccia, andesite 2 Swift Street 3 Chert

Kennedy Dominantly pillow and massive basalt, rare dolerite E dykes, but also contains mudstone, sandstone and N stratabound metalliferous rocks O an crust Watonga Serpentinite 4 t Z lt oce (Not separately mappable away from coastal exposure.) her Basa Formation d c N free Dominantly chert an I O Shelly Beach ts Undifferentiated rocks: slate, chert, mudstone, Mantle en T sandstone, conglomerate, and minor basalt and im C Drive d stratabound metalliferous rocks e U Mantle S D Koala Street B Drive U Port Macquarie Serpentinite S Massive, schistose serpentinite, rodingite, serpentinised peridotite, and orthopyroxenite

Pacific Port Macquarie Serpentinite 5 Transit ‘Inferred from drilling Hill Miners Beach Road Rocky Beach Metamorphic Mélange: eclogite, omphacitite, blueschist, glaucophane–phengite Ridge Parsons schist, tremolite marble and rare slate

Ocean Road

River, creek,dam N Seawall Drive  0 0.5 1 km Drive  Tacking Lighthouse Flinders Lighthouse Point Blueschist + eclogite Serpentinite Sediments Chert Basalt Beach Matthew (Och et al., 2007) 5 4 3 2 1 www.resourcesandenergy.nsw.gov.au 1 Volcanoes under the sea 2 Death on the seafloor 3 Sediments move from land to sea 4 Down the subduction zone 5 Rare rocks from deep Earth

Breakwall At southern Shelly Beach, you can see rocks formed at the start In the middle of Shelly Beach, rocks called chert formed part On the northern side of Nobby Head, we are mid-way along The rocks at Flynns Beach descended into the earth down a Look down on Rocky Beach from the clifftop. The rocks on the of their plate tectonic journey across the ocean. Ocean crust is way along their plate tectonic journey. After the ocean crust the geotrail. The ocean plate was also mid-way along its subduction zone and affected the mantle rocks around them. beach represent the end of the plate tectonic journey. Around Town Beach mostly formed from a dark, fine-grained volcanic rock called basalt (Stop 1) was formed, it travelled away from the mid- tectonic journey, nearing a subduction zone and a chain of The original mantle material surrounding the basalt was 460–490 million years ago, after travelling thousands of Town Beach Park basalt. This type of rock forms in mostly underwater (or ocean ridge and began to collect sediment on top. This volcanoes. Here, sediments were eroded from the volcanoes transformed into a rock called serpentinite, which has a soft kilometres across the ocean, these rocks were dragged down submarine) volcanoes in places like the mid-ocean ridge. On sediment mainly formed from tiny marine organisms such as and deposited nearby in the ocean. The sediments were greasy feel and is commonly bright green. This colour is due to (or subducted) as part of a crustal plate to depths around 104 southern Shelly Beach the basalt flowed out of submarine radiolarians that lived near the surface of the ocean. After transported by gravity-driven (or turbidity) currents downslope the original dark mantle minerals transforming into greenish km below the surface, and to temperatures around 570°C. ALBAN PL volcanoes as molten lava that cooled in the shape of pillows. death, their skeletons rained down on the sea floor. They into a trench, where they accumulated with the marine cherts in minerals such as lizardite and antigorite as a result of heat and We know subduction happened at Rocky Beach due to the Sometime after the first cooling episode, new molten basalt collected in layers above the basalt. These layers formed from deposits called turbidites. water produced during subduction. Serpentinite was formed special rocks and minerals found here. They only occur deep STEWART ST was injected into the ocean floor crust as long, thin fingers variations in the type and amount of marine skeletons and the Trenches lie next to chains of volcanoes either in oceanic or at depths of 1–60 km, where pressures are low but in subduction zones and include blueschist and eclogite. called dykes. In some locations, basalt first cooled slowly deep amount of external sediment added. When thick layers of continental areas and are the deepest parts of the ocean. After temperatures are relatively high (350–600°C). Due to stress in They are very rare to find on Earth’s surface today. Blueschist is in the earth forming big shiny feldspar crystals, before later sediment built up, pressure and chemical changes converted the earth, or shearing, the serpentinite has a strongly aligned a deep blue colour and has beautiful minerals such as PACIFIC DR Flagstaff Hill leaving the trench area, the ocean plate and the sediments

OWEN ST flowing out onto the seafloor and forming the smaller the fossil skeletons into the rock we call chert. As the chert was texture called cleavage. It also contains unsheared, large dark phengite, which has been folded during the subduction LORD ST riding on it descended into the subduction zone, where they surrounding dark crystals. transported towards the trench, it commonly slumped and slid, experienced increased heat and particularly pressure. There fragments of the transformed mantle, making it look like green event. Eclogite is an emerald green rock composed of forming sinuous folds. Fossils known as conodonts (jaw they underwent slumping, sliding, folding and faulting. To see fruit cake on cliff faces. Serpentinite is exposed at the southern attractive minerals such as omphacite and lawsonite. Oxley Beach Oxley oval structures of oceanic eel-like animals) can be used to date the the sediments, walk 80 m down the path to the headland at the headland of Flynns Beach. chert, which at Port Macquarie is around 460 million years old. GORDON ST southern end of Nobby Beach.

Windmill Hill Reserve BURRANWAN ST WINDMILL ST 5 0.5 km 3.4 km

HOME ST PORT Rocky Beach Basalt pillows (two outlined) on southern Shelly Beach. MACQUARIE A boulder on Rocky Beach that contains blueschist (blue) mixed HILL ST with eclogite (green). The blueschist contains small folds. Serpentinite outcrop at the southern end of Flynns Beach, showing the green serpentine minerals and the darker, massive blocks of ARNCLIFFE AV Skeletons of modern radiolarians. Human hair on bottom for scale. On the northern side of Nobby Head is a mix of turbidite sediments serpentinite called phacoids. Tasman Sea Radiolarians from 460 million years ago look very similar, and when and chert. The grey rock has alternating coarse- and fine-grained ELIZABETH ST compressed they form chert. Image source: Sarah Kachovich, sedimentary layers; the chert is mostly brown. During subduction, University of Queensland. EVERARD ST both rock types were strongly deformed and mixed together.

T Macquarie U P

P

Nature Reserve E N

N

Y

RD Flynns Beach

1.8 km FLYNN ST 4 2.1 km

Tourist Drive 10 A thin basalt dyke (outlined in red) that injected into older pillow mm Nobbys Beach basalts. Blueschist seen under a microscope, showing colourful phengite OCEAN ST P minerals. The crystals were folded during subduction, as shown by A C the red dashed lines. IF IC 2.3 km Shearing during fault movement led to the serpentinite forming D R 3 1.6 km cleavage – a curved alignment of crystals traced out by the dashed red lines. The basalt/chert boundary at Stop 2, shown by a red dashed line Strongly folded chert (brown) and mudstone (grey) are exposed on SWIFT ST K Nobby Head with chert above, is where the top of the ocean plate was located ENNY DR the rock platform. These deposits consist of skeletons of tiny marine 460 million years ago. creatures (chert) and sediments eroded from the land nearby (mudstone). The layers were folded during subduction. John Downes Park

DIXON AV

LEANDA ST

Caution: Access at this point can be affected by high tides and beach erosion. No dogs south of this point. This dyke (centre) squeezed through older, colder basalt. As it cooled, the edge cooled faster than the middle. This ‘chilled margin’ has a finer grain size and a darker colour than the middle. The red crystals in this green eclogite are a few millimetres across. They are garnets, and only form in high temperature and pressure 500 m situations, such as 104 km below the surface and at 570°C. Under a microscope, blade-like crystals of antigorite can be seen Shelly Beach cutting older crystals of another serpentine mineral, lizardite. These minerals help tell us the temperatures and pressures at which the Folded chert at Shelly Beach, showing zig-zag folds formed by rock formed. Harry’s slumping on the seafloor. Bands of mudstone (dark) and siltstone (light) formed from gravity Lookout 3.6 km flows that transported fine-grained sediments down slope from land into deep water. Each siltstone to mudstone layer is one flow event. Port Macquarie Coastal Geotrail 0.3 km

Geotrail Public toilet 2

Coastal walk Parking 3.9 km 1 0 km

Access track Bottle bubbler D R mm LLY Large shiny feldspar crystals in fine-grained basalt at Shelly Beach. HE B H S E A C Geotrail stop Eclogite seen under a microscope, showing high pressure and high 1 Stairs temperature minerals such as brown garnet (G), silver phengite (Ph) and grey glaucophane (Gl). Source: David Och. Geotrail start/end 2.3 km Sea Acres mm PACIFIC DR Rainforest Centre Walking distance Conodont fossil from chert at Port Macquarie used to date the rocks This microscope view shows a big fibrous crystal of the serpentine as around 460 million years old (from Och et al., 2007). Each mm mineral lizardite. However it has retained the shape of its original 0 250 500 1000 source mineral (orthopyroxene), enabling us to identify its origin in Sea Acres conodont is around half a millimetre long. Microscope photo of turbidite layers. The pale, coarse-grained National Park the mantle. Source: David Och. layers are silts and sands and the browner colours are mud, all metres composed of volcanic rock fragments.